Experimental Investigation of Factors Affecting the Injectability of Microcement Grouts

The paper illustrates some of the results obtained from an extensive experimental program, conducted on grouts manufactured with a pozzolanic microcement (D₉₈ = 10 μm) and an acrylic-based superplasticizer, and consisting of: a) injection tests in laboratory prepared sand columns, and b) rheological tests performed employing a high resolution rheometer. The data presented in the paper highlights the effects of varying the water-cement ratio of the mixtures (w/c = 1 to 2.75), the admixture dosage, (0–1.6% in terms of active polymer by mass of cement) and the injection pressure (p_inj = 50 and 200 kPa). An attempt is made to link the results of the injection tests to the rheological properties of the grouts. It is found that, for the reference medium investigated (Ticino sand), at a given injection pressure, provided that the viscosity exceeds a threshold value, there is a unique and linear relationship between the height penetrated by the grout inside the sand column and its viscosity. A similar relationship, albeit shifted to higher values of the viscosity, applies for a lower injection pressure. Small changes in the viscosity of the grout dramatically affect the height of sand permeated by the grout. Medium-related effects are also addressed. Based on the results of injection tests in five sands it is observed that small changes in the sand's gradation significantly affect its groutability, with increasing difficulties associated with grouting less uniform sands. Overall, the height penetrated by the grout correlates with the hydraulic conductivity of the medium.